Signal predistortion in radio transmitter

1. A method, comprising: receiving a transmission signal to be transmitted and a signal modeling a power supply voltage applied to a power amplifier; associating an envelope of the received transmission signal and the signal modeling the power supply voltage with predistortion information comprised in a distortion lookup table, wherein the information in the distortion lookup table is obtained beforehand from transmission signal distortion properties of the power amplifier and remains substantially fixed over time, predistorting the received transmission signal according to the associated predistortion information in order to compensate for distortion caused by the power amplifier; and scaling the envelope of the received transmission signal according to at least the received transmit power control commands and amplitude distortion lookup table to adjust the envelope of the transmission signal to a desired operational range of the power amplifier.

2. The method of claim 1 , wherein the distortion lookup table is an amplitude distortion lookup table comprising envelope predistortion information previously obtained from amplitude distortion properties of the power amplifier, the envelope predistortion information remaining substantially fixed over time, and predistorting the envelope of the received transmission signal according to the associated envelope predistortion information in order to compensate for amplitude distortion caused by the power amplifier.

3. The method of claim 2 , wherein the amplitude distortion lookup table comprises predistorted envelope signal values as a function of the envelope of the received transmission signal and the signal modeling the power supply voltage, the method further comprising: creating a predistorted envelope of the received transmission signal from the amplitude distortion lookup table values corresponding to the values of the envelope of the received transmission signal and the signal modeling the power supply voltage.

4. The method of claim 2 , further comprising: associating the envelope of the received transmission signal and the signal modeling the power supply voltage with phase predistortion information comprised in a phase distortion lookup table wherein the information in the phase distortion lookup table is obtained from phase distortion properties of the power amplifier, the information remaining substantially fixed over time; predistorting a phase of the received transmission signal according to the associated phase predistortion information in order to compensate for the phase distortion caused by the power amplifier, and combining the predistorted envelope and the predistorted phase of the transmission signal into the predistorted transmission signal before outputting the predistorted transmission signal for power amplification.

5. The method of claim 4 , wherein the predistorted envelope of the received transmission signal and the signal modeling the power supply voltage is associated with the phase predistortion information.

6. The method of claim 4 , further comprising: obtaining the phase predistortion information of the phase distortion lookup table by measuring beforehand the phase distortion caused by the power amplifier as a response to given values of a voltage of an input transmission signal to be power-amplified and to a power supply voltage.

7. The method of claim 4 , wherein the phase distortion lookup table comprises values indicating the amount of phase distortion caused by the power amplifier as a function of the envelope of the received transmission signal and the signal modeling the power supply voltage, the method further comprising: predistorting the phase of the received transmission signal by subtracting the phase distortion caused by the power amplifier from the phase of the received transmission signal.

8. The method of claim 1 , further comprising: obtaining the predistortion information of the distortion lookup table by measuring the distortion caused by the power amplifier as a response to given values of the voltage of an input transmission signal to be power-amplified and to an input power supply voltage.

9. The method of claim 1 , further comprising: producing the signal modeling the power supply voltage to track the envelope of the transmission signal; filtering the signal modeling the power supply voltage with a non-linear filter which preserves the rise time of the signal and lengthens the fall time of the signal, and using the filtered signal modeling the power supply voltage when associating the received signals with the amplitude distortion.

10. The method of claim 1 , further comprising: producing the signal modeling the power supply voltage to track the envelope of the transmission signal; filtering the signal modeling the power supply voltage with a filter having a frequency response of a power supply signal generator providing the power amplifier with the power supply voltage, and using the filtered signal modeling the power supply voltage when associating the received signals with the amplitude distortion.

11. The method of claim 1 , further comprising: producing the signal modeling the power supply voltage to track the envelope of the transmission signal; filtering the signal modeling the power supply with a low-pass filter having a corner frequency lower than that of a power supply voltage generator providing the power amplifier with the power supply voltage, and using the filtered signal modeling the power supply voltage when associating the received signals with the amplitude distortion.

12. The method of claim 1 , further comprising: producing the signal modeling the power supply voltage to track the envelope of the transmission signal; synchronizing the signal modeling the power supply voltage with the predistorted transmission signal; providing the power amplifier with the power supply voltage from a power supply voltage generator controlled by the signal modeling the power supply voltage; power-amplifying the predistorted transmission signal with the power supply voltage synchronized with the predistorted transmission signal, and transmitting the power amplified transmission signal.

13. The method of claim 1 , further comprising: selecting the distortion lookup table according to at least one of the following criteria: the transmission frequency of the transmission signal, or the temperature of the power amplifier.

14. An apparatus, comprising: a predistortion unit comprising an interface to receive a transmission signal to be transmitted and a signal modeling a power supply voltage applied to a power amplifier, the predistortion unit being configured to associate an envelope of the received transmission signal and the signal modeling the power supply voltage with predistortion information comprised in a distortion lookup table, wherein the information in the distortion lookup table is obtained from the transmission signal distortion properties of the power amplifier, the predistortion information remaining substantially fixed over time, and to predistort the received transmission signal according to the associated predistortion information in order to compensate for the distortion caused by the power amplifier, and wherein the predistortion unit is further configured to scale the envelope of the received transmission signal according to at least the received transmit power control commands and amplitude distortion lookup table to adjust the envelope of the transmission signal to a desired operational range of the power amplifier.

15. The apparatus of claim 14 , wherein the distortion lookup table is an amplitude distortion lookup table comprising envelope predistortion information obtained from amplitude distortion properties of the power amplifier and remaining substantially fixed over time and wherein the predistortion unit is further configured to predistort the envelope of the received transmission signal according to the associated envelope predistortion information in order to compensate for the amplitude distortion caused by the power amplifier.

16. The apparatus of claim 15 , wherein the amplitude distortion lookup table comprises predistorted envelope signal values as a function of the envelope of the received transmission signal and the signal modeling the power supply voltage, and the predistortion unit is further configured to create the predistorted envelope of the received transmission signal from the amplitude distortion lookup table values that correspond to the values of the envelope of the received transmission signal and the signal modeling the power supply voltage.

17. The apparatus of claim 15 , wherein the predistortion unit is further configured to associate the envelope of the received transmission signal and the signal modeling the power supply voltage with phase predistortion information comprised in a phase distortion lookup table wherein the information in the phase distortion lookup table is obtained from phase distortion properties of the power amplifier, the phase distortion information remaining substantially fixed over time, to predistort the phase of the received transmission signal according to the associated phase predistortion information in order to compensate the phase distortion caused by the power amplifier, and to combine the predistorted envelope and the predistorted phase of the transmission signal into the predistorted transmission signal before outputting the predistorted transmission signal for power amplification.

18. The apparatus of claim 17 , wherein the predistortion unit is further configured to associate the predistorted envelope of the received transmission signal and the signal modeling the power supply voltage with the phase predistortion information.

19. The apparatus of claim 17 , wherein phase predistortion information of the phase distortion lookup table indicating the phase distortion caused by the power amplifier as a response to given values of the voltage of an input transmission signal to be power amplified and a power supply voltage is stored into the predistortion unit beforehand.

20. The apparatus of claim 17 , wherein the phase distortion lookup table comprises values indicating the amount of phase distortion caused by the power amplifier as a function of the envelope of the received transmission signal and the signal modeling the power supply voltage, and the predistortion unit is further configured to predistort the phase of the received transmission signal by subtracting a phase distortion caused by the power amplifier from a phase of the received transmission signal.

21. The apparatus of claim 14 , wherein the predistortion information of the distortion lookup table indicates the transmission signal distortion caused by the power amplifier as a response to given values of the voltage of an input transmission signal to be power amplified, and a power supply voltage is stored into the predistortion unit.

22. The apparatus of claim 14 , further comprising: the power amplifier configured to amplify the predistorted transmission signal; a power supply voltage generator configured to provide the power amplifier with a power supply voltage; an envelope tracking unit configured to detect an envelope of the received transmission signal and produce the signal modeling the power supply voltage and tracking an envelope of the transmission signal, and a low-pass filter, wherein the low-pass filter includes a corner frequency lower than that of the power supply voltage generator.

23. The apparatus of claim 14 , further comprising: the power amplifier configured to amplify the predistorted transmission signal; a power supply voltage generator configured to provide the power amplifier with a power supply voltage; an envelope tracking unit configured to detect an envelope of the received transmission signal, and produce the signal modeling the power supply voltage and tracking an envelope of the transmission signal; a filter having a frequency response matched to that of at least the power supply signal generator, the filter being configured to filter the signal modeling the power supply voltage and output the filtered signal modeling the power supply voltage to the predistortion unit.

24. The apparatus of claim 23 , wherein the envelope tracking unit is further configured to output the signal modeling the power supply voltage to the filter as a control signal to the power supply voltage generator.

25. The apparatus of claim 14 , further comprising: the power amplifier configured to amplify the predistorted transmission signal; a power supply voltage generator configured to provide the power amplifier with a power supply voltage; a power tracking unit configured to detect the power of the received transmission signal, produce the signal modeling the power supply voltage and tracking the power of the transmission signal, and a low-pass filter having a corner frequency lower than that of the power supply voltage generator.

26. The apparatus of claim 14 , further comprising a distortion lookup table selection unit configured to select the distortion lookup table according to at least one of the following criteria: a transmission frequency of the transmission signal, or a temperature of the power amplifier.

27. The apparatus of claim 14 , further comprising: an envelope tracking unit configured to produce the signal modeling the power supply voltage to track the envelope of the transmission signal and to filter the signal modeling the power supply voltage with a non-linear filter which preserves the rise time of the signal and lengthens the fall time of the signal, wherein the predistortion unit is further configured to use the filtered signal modeling the power supply voltage when associating the received signals with the amplitude distortion.

28. A radio transmitter comprising: a predistortion unit including an interface to receive a transmission signal to be transmitted and a signal modeling a power supply voltage applied to a power amplifier, the predistortion unit being configured to associate an envelope of the received transmission signal and the signal modeling the power supply voltage with predistortion information included in a distortion lookup table, wherein the predistortion information in the distortion lookup table is obtained from the transmission signal distortion properties of the power amplifier, the predistortion information remaining substantially fixed over time, and to predistort the received transmission signal according to the associated predistortion information in order to compensate for the distortion caused by the power amplifier, and wherein the predistortion unit is further configured to scale the envelope of the received transmission signal according to at least the received transmit power control commands and amplitude distortion lookup table to adjust the envelope of the transmission signal to a desired operational range of the power amplifier.

29. An apparatus, comprising: receiving means for receiving a transmission signal to be transmitted and a signal modeling a power supply voltage applied to a power amplifier; associating means for associating an envelope of the received transmission signal and the signal modeling the power supply voltage with predistortion information comprised in a distortion lookup table, wherein the predistorton information in the distortion lookup table is obtained from transmission signal distortion properties of the power amplifier and remains substantially fixed over time, predistorting means for predistorting the received transmission signal according to the associated predistortion information in order to compensate the distortion caused by the power amplifier; and scaling means for scaling the envelope of the received transmission signal according to at least the received transmit power control commands and amplitude distortion lookup table to adjust the envelope of the transmission signal to a desired operational range of the power amplifier.

30. A computer program embodied on a computer-readable medium comprising computer code readable by a computer for executing a computer process for transmission signal predistortion, the process comprising: receiving a transmission signal to be transmitted and a signal modeling a power supply voltage applied to a power amplifier; associating an envelope of the received transmission signal and the signal modeling the power supply voltage with predistortion information comprised in a distortion lookup table, wherein the predistortion information in the distortion lookup table is obtained from transmission signal distortion properties of the power amplifier and remains substantially fixed over time, predistorting the received transmission signal according to the predistortion information in order to compensate for the distortion caused by the power amplifier; and scaling the envelope of the received transmission signal according to at least the received transmit power control commands and amplitude distortion lookup table to adjust the envelope of the transmission signal to a desired operational range of the power amplifier.

31. The computer readable medium of claim 30 , wherein the computer-readable medium comprises at least one of a program storage medium, a record medium, a computer readable memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, or a computer readable compressed software package.